<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title>非数值Na</title>
	</head>
	<body>
		<script>
			var a=1;
			var b;
			console.log(typeof(1));
			console.log(typeof(b));
			console.log(a+b);
			b="b";
			console.log(a+b);
			
			
		</script>
	</body>
</html>
